1. Field of the Invention
The present invention relates to a gas-fired heating apparatus or heater comprising at least one atmospheric gas burner, which is arranged within a partially or completely closed combustion chamber and which is associated with a complete premixing gas/air supply system with a fuel gas feed nozzle, whose inlets for fuel gas and combustion air are arranged on the heater outside of the combustion chamber.
2. Related Art
This sort of gas-fired heating apparatus, to which the invention relates, is typically a gas-fired hot water heater or a gas-fired heating apparatus, like those used for industrial heating units or household fireplaces.
Gas-fired hot water heaters are in use in many different embodiments and power stages in different applications both in the private and industrial sectors.
This sort of gas-fired not water heater prepares hot water for industrial use or for household or industrial applications.
The so-called “water heater” marketed in the USA is a special embodiment of this sort of gas-fired hot water heater, which produces water for showers or the like in the workplace or other places. For example, a “water heater” is described in U.S. Pat. No. 4,953,510, which comprises a water tank for storing the heated water. This water tank is combined with a device for heating water in the water heater. The device for heating the stored water comprises an open atmospheric gas burner. The hot exhaust gas including the combustion products from the gas burner acts on the bottom of the water tank and subsequently rises through an elongated exhaust flue, which extends through the center section of the water tank. In this type of water heater the hot gas flowing upward in the exhaust flue comes into contact with the interior surfaces of the exhaust pipe, while the water in the water tank is in contract with the outer surfaces of the pipe. While the combustion proceeds, the water within the water tank is heated by heat conduction through the wall of the exhaust flue. In this type of water heater normally a longitudinal separating wall is arranged within the exhaust pipe in order to improve the efficiency of the heat transfer through the wall of the exhaust pipe from the hot combustion gas to the water within the water tank. Further this sort of water heater can have a thermally activated valve, which stops the combustion at the gas burner, when the temperature of the water in the water tank reaches a predetermined temperature.
In order to reduce heat loss from the water heater both during the heating of the water and also after halting the combustion process, the outer surface of the water tank is usually covered with a thermal insulation material.
Increasingly strict legal regulations regarding avoiding accidents, especially when combustible vapors arrive in the open combustion region, and in regard to improvement of exhaust gas content, have led to developments in the water heater field, which provide a nearly completely closed combustion (burner) chamber, in which a premixing gas burner, a so-called pre-mix burner, is arranged.
This sort of water heater is described in U.S. Pat. No. 5,875,739. The structure and arrangement of the prior art pre-mix burner in the closed combustion chamber is shown in FIG. 4 of the present application, which is taken from the above-mentioned U.S. Patent. This figure is a cross-sectional view of a water heater with a water tank 1 and a nearly closed combustion chamber 2, to which an exhaust flue 3 is connected, which extends through the center of the water tank 1. The combustion chamber 2 and the water tank 1 are insulated from the surrounds by thermal insulation 4. An atmospheric pre-mix burner 5 is arranged in the combustion chamber 2, which comprises a mixing chamber 6 and a spherical burner mat 7. A Venturi 8 is connected to the mixing chamber 6, which extends through the thermal insulation 4 until at the outer surface of the water heater. A nozzle 10 for supplying the fuel gas is arranged within the outer opening of the Venturi. Primary air is drawn through the outer opening 9 while fuel gas flows into the Venturi 8, which is then mixed by turbulence with the fuel gas in the mixing chamber 6.
Another embodiment of a water heater with a complete premixing atmospheric gas burner is described in U.S. Patent Application 2003/0111 023 A1. This known gas burner 5 is constructed with a planar rectangular burner mat, as shown in FIG. 5 of the present application, which is taken from this U.S. Patent Application. This figure shows the mixing chamber 6 formed together with the Venturi 8. The Venturi 8 has an inlet 10′ for fuel gas and the entrance opening 9 for primary air.
It has been shown that the pressure behavior in the combustion chambers of gas-fired heaters with atmospheric, complete premixing gas burners in a nearly completely closed combustion chamber produces resonances, which put the system into oscillation. These resonance oscillations have the following disadvantages:                no stable or uniform combustion with reduced flue gas quality is possible,        noticeable troublesome loud sound is produced,        back fire of the flames through the combustion medium is possible, depending on the turbulence in the combustion chamber.        